Its trickier to get as effiecient burn in a petrol because gas position is different, and you may have to tweak it during acceleration (correct if I am wrong). In a diesel simple pedal to the medal attitude brings best fuel efficiency if certain facts are met. So in a diesel you dont have to adjust the nut so much...
What I wrote applies almost all turbo diesels, but some in some cars the torgue peak is higher. Steady throttle and highest gear if drived steady speed is also a efficient choice but still the accelerations to target speed/posted speed limit should be:
1. Done at torgue peak or close to it
2. Using shortest gear possible so without revving it over 2500 rpm or 3000 rpm. This depends on the car. On my lupo 3L the electromanual gearbox in eco mode car computer uses gears so that it starts the acceration at 2000 rpm and shifts bigger gear in 3000 rpm. On my lupo almost nothing happens under 2000 rpm. I believe that engineers protect in my lupo the gearbox in lower rpm range. You can hear and feel when engine reaches 2000 RPM. Noise changes from baaam to BAAAAAAM if you know what I mean
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On the lupo if I am doing P&G the speed drops to 74 km/h the engine will put the third gear in because in fourth the RPMs drop under 2000 RPM where nothing happens. At 83 it already changes to fourth. So in that speed range manual would be better because it also takes fuel at least in the lupo to change gears.
Effect of the driving technigue can easily be tested on short test route. It does not have to be long 6 miles or so. Your 09 VW will show quite accurate readings with different driving technigues. Keep the test speed close to 50 MPH so aero does not play so big role.
1. First steady throttle like you drive at the moment from 0-50 and keep it there
2. Second trip that with rapid acceleration to target speed and steady speed
3. third rapid acceleration and to target speed +7 MPH coast so that you lose 16 MPH and again a push.
My estimation of the results are
1. Is worse
2. is 4% better
3. is 15% better
BR:Vesa